Wideband Sensor Research Articles

On the influence of vacuum on the design and characterization of MEMS

The article will be focused on the influence of vacuum on resonant micro electromechanical sensor and actuator systems (MEMS). The system’s encapsulation with a pressure below atmospheric pressure plays a key role in the sensor performance especially in the field of vibration sensors. These sensors are becoming increasingly important for structural health or wear state monitoring in many engineering applications. Structural health, wear states and damage levels can be recognized by means of the vibration spectrum generated by propagating sound waves in solid materials known as ‘acoustic emission’. Commonly the vibration spectrum is measured by wide band accelerometers and subsequent Fourier transformation. Alternatively mechanical vibrations can be detected by resonant sensor systems. In particular these can be arrays of tiny cantilevers with multiple fixed Eigenfrequencies or single resonators with tunable Eigenfrequencies. Advantages of resonant pick-up compared to wide band sensors are the inherent spectral filtering and signal amplification in the mechanical domain due to the high quality factor at resonance. Therefore, an important design parameter is viscous damping of moving silicon cantilevers in the surrounding gas (e.g. air). The theoretical background of fluid–structural interactions and methods for experimental characterization of damping properties at atmospheric pressure and in evacuated environment will be presented. Measurements using a vacuum wafer prober for electrostatic actuation and optical motion sensing were conducted.

Micromechanics of asperity rupture during laboratory stick slip experiments

[1] Acoustic emissions and tremor-like signals are widely recorded in laboratory experiments. We are able to isolate the physical origins of these signals using high resolution nanoseismic analysis. The use of a picometer-sensitive, wide-band sensor array permits us to determine force-time functions and focal mechanisms for discrete events found amid the “noise” of friction, similar to how low frequency earthquakes are found buried within tremor. We interpret these localized events to be the rupture of μm-sized contacts, known as asperities. We performed stick-slip experiments on plastic/plastic and rock/rock interfaces and found a systematic difference between the nano earthquakes: the rock interface produces very rapid (<1 μs) implosive forces indicative of brittle failure and fault gouge formation, while rupture on the plastic interface releases only shear force and produces a nano quake more similar to earthquakes commonly recorded in the field. The difference between the mechanisms is attributed to the vast differences in the hardness and melting temperatures of the two materials, which affect the distribution of asperities as well as their failure behavior. With proper scaling, the strong link between material properties and laboratory earthquakes will aid in our understanding of fault mechanics and the generation of earthquakes and tectonic tremor.

Upper Bounds on Lifetime of Ordinary Clustering Ultra Wide Band Sensor Networks

考虑了En</em> 个传感节点和一个Sink 组成的跳时脉冲无线电超宽带(time hopping impulse radio ultra wideband,简称TH-IR UWB)传感网,其中,n 个传感节点均匀且独立地分布在正方形上.分别推导了常规分簇的密集和扩展TH-IR UWB 传感网的生存期上界.常规分簇网络的簇头仅对本簇内的节点发送的数据进行融合,而对其他簇头发送的数据仅转发.研究结果表明,常规分簇密集TH-IR UWB 传感网的生存期上界与节点密度(或节点数)成正比,扩展网络的生存期上界与部署区域大小(或节点数)成反比.研究结果也表明,对于密集网络,理想情形下的生存期上界比静态网络提高了(<em>n</em>/log<em>n</em>)^1/2 倍;而对于扩展网络,理想情形下生存期的上界比静态网络提高了(<em>λn</em>/log(<em>λn</em>))^1/2 倍.因此,节点或Sink 在正方形内随机移动能够提高传感网生存期.;This paper considers the time hopping impulse radio ultra wide band (TH-IR UWB) sensor networks, with <em>n</em> sensor nodes uniformly and independently located on a square and a Sink. The upper bounds on the lifetime of ordinary clustering dense and extended TH-IR UWB sensor networks are derived respectively. For ordinary clustering networks, the cluster head aggregates data from the nodes within its own cluster, and relays data to other cluster heads. The results indicate that the upper bounds on the lifetime of ordinary clustering dense TH-IR UWB are in proportion with the node density (or the number of nodes), while the upper bounds on the lifetime of extended networks are inversely proportional to the size of the deployment area (or the number of nodes). The results also reveal that the upper bound on the lifetime of dense network in the ideal case are longer than those of the static network by a factor of (<em>n</em>/log <em>n</em>)^1/2, and the upper bound on the lifetime of extended network in the ideal case are longer than those of the static network by a factor of (<em>λn</em>/log(<em>λn</em>))^1/2. Therefore, sensor nodes, or the Sink moving randomly in the square, can improve the lifetime of ordinary clustering TH-IR UWB sensor network.

Automated Trajectory and Path Planning Analysis Based on Ultra Wideband Data

This work studies the utility of ultra wideband (UWB) sensor technology for optimizing construction site operations. In particular, recorded trajectory signals provide important behavioral information regarding site usage that can be exploited for planning and logistical purposes. Here, post processed trajectory information from UWB signals populate an occupancy grid, which is a spatial histogram of workers, travel patterns. The occupancy grid is used for path planning and serves two purposes. The first suggests optimal paths for workers while the second generates optimal paths for vehicles. The path generation algorithm provides multiple paths, and optimality scores for a variety of path metrics, including distance, time, and worker sparsity. To generate the optimal paths, a path planning graph is generated from the occupancy grid and any automatically determined or manually specified obstacles. The algorithm applies equally to any mobile, major construction resource: workers, equipment, and materials that are tagged with a UWB tag. Vital statistics obtained from the calculated paths provide important operational information to site operations and safety managers.

High-resolution imaging of dielectric profiles by using a time-domain ultra wideband radar sensor

This paper describes the development of an imaging instrument that capitalizes on high-resolution phenomenon in inverse scattering using a time-domain ultra wideband (UWB) sensor. The image reconstruction algorithm that accounts for the band-limited view of the UWB data is based upon the TM-mode wave equation, the Born approximation, and the adjoint method for computing the Fréchet derivatives. The computation of the sensitivity function requires the forward propagation of the UWB wavefield, as well as the reverse propagation of the residual wavefield. The electromagnetic and adjoint fields are calculated using the finite-difference time-domain (FDTD) method, implementing the first and second orders Mur’s absorbing boundaries. The overall performance of the instrumentation system is demonstrated using computer simulations and experimental measurements. Results indicate that the equipment can reconstruct fairly complicated dielectric profiles at near millimeter resolution even with the presence of large amount of noise.

Interferometric fiber optic sensors for biomedical applications of optoacoustic imaging

We present a non-metallic interferometric silica optical fiber ultrasonic wideband sensor for optoacoustic imaging applications. The ultrasonic sensitivity of this sensor has been characterized over the frequency range from 1 to 10 MHz. A comparative analysis has been carried out between this sensor and an array of piezoelectric transducers using optoacoustic signals generated from an optical absorbent embedded in a tissue mimicking phantom. Also, a two dimensional reconstructed image of the phantom using the fiber interferometric sensor is presented and compared to the image obtained using the Laser Optoacoustic Imaging System, LOIS-64B. The feasibility of our fiber optic based sensor for wideband ultrasonic detection is demonstrated.

Acoustic emission method as a tool of partial discharges indication

The present paper deals with a method of tracking the partial discharges using the acoustic emission method. The quantity under study was the overshoot counting rate in acoustic emission signals. The subject of the experiment was a high-voltage generator rod, which had been provided with Relanex insulation. Acoustic signals, which were generated in the Relanex insulation layer, were picked up by wide-band sensors. Measurement results proved that electric discharges in a cavity are accompanied by the generation of mechanical oscillations, which in turn act as a source of standing waves in the cavity and standing waves in the rod and the insulator. The frequency spectrum therefore extends from the rod fundamental oscillation mode (i.e., 3 kHz) up to the cavity natural frequencies (in the order of several MHz).

Relationship between office workers’ staying and workstation attributes in a non-territorial office using ultra wide band sensor network

This paper investigates the staying and moving characteristics of office workers in a non-territorial office using an ultra wide band (UWB) impulse radio sensor network. The differences between office workers’ staying and moving are clarified according to the individual workstation type that they select. The study determines the characteristics of each type of workstation. By clarifying office workers’ preference for staying and moving with regard to individual workstation types and office worker post, the reasons why office workers in different posts tended to select different types of workstations were revealed. Specifically, leaders tended to select workstations at the “inner meeting corner side” most frequently, as they had a greater need to stay in other areas. In contrast, ordinary staff needed to visit office workers in other areas less often, and as such, they tended to select individual workstations at the “middle meeting corner side.” Barring this, they tended to select individual workstations at the “middle corridor side” or “outer-meeting corner side.” Temporary staff members had little need to visit or stay at other places so they tended to select individual workstations at the “window side,” which is seldom visited or stayed at by other office workers and they could be disturbed less often from their solo work.

Infrared Thermography and Acoustic Emission in 2D Plain Woven C/Sic Composites under Tensile-Tensile Fatigue Loading

Plain plate specimens of 2D plain woven C/SiC composites were performed on Instron8801. Infrared (IR) thermography was recorded using an infrared camera. Acoustic emission (AE) signal was detected by two AE wide band sensors attached on specimen. They were measured synchronously and real-timely. Thermal dissipation Q was deduced based on the first law of thermodynamics. When the applied stress was lower than fatigue endurance limit, Q rose in the early cyclic loading stage and then the rate of Q accumulation gradually approached a steady value as the proceeding cycles, conversely, Q rose quickly until led to failure of the composites. AE accumulated energy was discussed based on the AE data. Higher applied stress would cause more damage within the composites, and more AE signals were detected. Compared with damage calculated from modulus, Q and AE accumulated energy had fairly well agreement with the damage. It can be concluded that it is possible to employ these non-destructive evaluation methods as in-situ damage evolution indicators for 2D C/SiC composites.

Unexploded ordnance discrimination using magnetic and electromagnetic sensors: Case study from a former military site

In a study at a military range with the objective to discriminate potentially hazardous [Formula: see text] mortars from nonhazardous shrapnel, range, and cultural debris, six different discrimination techniques were tested using data from an array of magnetometers, a time-domain electromagnetic induction (EMI) cart, an array of time-domain sensors, and a time-domain EMI cart with a wider measurement bandwidth. Discrimination was achieved using rule-based or statistical classification of feature vectors extracted from dipole or polarization tensor models fit to detected anomalies. For magnetics, the ranking by moment yielded better discrimination results than that of apparent remanence from relatively large remanent magnetizations of several of the seeded items. The magnetometer results produced very accurate depths and fewer failed fits attributable to noisy data or model insuffi-ciency. The EMI-based methods were more effective than the magnetometer for intrinsic discrimination ability. The higher signal-to-noise ratio, denser coverage, and more precise positioning of the EM-array data resulted in fewer false positives than the EMI cart. When depth constraints from the magnetometer data were used to constrain the EMI fits through cooperative inversion, discrimination performance improved considerably. The wide-band EMI sensor was deployed in a cued-interrogation mode over a subset of anomalies. This produced the highest-quality data because of collecting the densest data around each target and the additional late time-decay information available with the wide-band sensor. When the depth from the magnetometer was used as a constraint in the cooperative inversion process, all [Formula: see text] mortars were recovered before any false positives were encountered.

A simple wide‐band gradiometer for operation in very low background field

AbstractA simple gradiometer, capable of sensing submicrotesla changes in magnetic field with 10‐μs resolution, is constructed from a pair of low‐cost, wide‐band Hall‐effect sensors output to a voltage preamplifier and digital storage oscilloscope. The linear operational range of the sensors (±7.5 mT) limits typical applications, such as gradient coil development and testing, to environments where background fields are very low. The gradiometer is ideal for characterizing gradient field rise times and waveforms in this limit and applications pertinent to very‐low‐field nuclear magnetic resonance and magnetic resonance imaging are presented. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 37B: 1–6, 2010

High-sensitivity ultrasound interferometric single-mode polymer optical fiber sensors for biomedical applications

This work describes the results of ultrasonic wideband sensors based on single-mode polymer optical fibers that may be used for biomedical applications. We have compared the ultrasonic sensitivities of two Mach-Zehnder interferometric intrinsic optical fiber sensors. One is based on a single-mode polymethylmethacrylate optical fiber and the second on single-mode silica optical fiber, both operating at 632.8 nm. At a frequency of 1 MHz these sensitivities are 13.1 and 0.85 mrad/kPa, respectively. The ultrasonic phase sensitivity of the polymer optical fiber is more than 12 times larger than that from the fused silica fiber in the 1-5 MHz range.

Steady-State Biodiesel Blend Estimation via a Wideband Oxygen Sensor

A substantial opportunity exists to reduce carbon dioxide (CO2) emissions, as well as dependence on foreign oil, by developing strategies to cleanly and efficiently use biodiesel, a renewable domestically available alternative diesel fuel. However, biodiesel utilization presents several challenges, including decreased fuel energy density and increased emissions of smog-generating nitrogen oxides (NOx). These negative aspects can likely be mitigated via closed-loop combustion control provided the properties of the fuel blend can be estimated accurately, on-vehicle, in real-time. To this end, this paper presents a method to practically estimate the biodiesel content of fuel being used in a diesel engine during steady-state operation. The simple generalizable physically motivated estimation strategy presented utilizes information from a wideband oxygen sensor in the engine’s exhaust stream, coupled with knowledge of the air-fuel ratio, to estimate the biodiesel content of the fuel. Experimental validation was performed on a 2007 Cummins 6.7 l ISB series engine. Four fuel blends (0%, 20%, 50%, and 100% biodiesel) were tested at a wide variety of torque-speed conditions. The estimation strategy correctly estimated the biodiesel content of the four fuel blends to within 4.2% of the true biodiesel content. Blends of 0%, 20%, 50%, and 100% were estimated to be 2.5%, 17.1%, 54.2%, and 96.8%, respectively. The results indicate that the estimation strategy presented is capable of accurately estimating the biodiesel content in a diesel engine during steady-state engine operation. This method offers a practical alternative to in-the-fuel type sensors because wideband oxygen sensors are already in widespread production and are in place on some modern diesel vehicles today.

Feasibility study of wide-band low-profile ultrasonic sensor with flexible piezoelectric paint

This paper presents a feasibility study of flexible piezoelectric paint for use in wide-band low-profile surface-mount or embeddable ultrasonic sensor for in situ structural health monitoring. Piezoelectric paint is a piezoelectric composite with 0-3 connectivity. Because of its ease of application, piezoelectric paint can be readily fabricated into sensing element with complex pattern. This study examines the characteristics of piezoelectric paint in acoustic emission signal and ultrasonic guided wave sensing. A series of ultrasonic tests including pitch catch and pencil break tests were performed to validate the ultrasonic wave sensing capability of piezoelectric paint. The results of finite element simulation of ultrasonic wave propagation, and acoustic emission generated by a pencil lead break on an aluminum plate are also presented in this paper along with corresponding experimental data. Based on the preliminary experimental results, the piezoelectric paint appears to offer a promising sensing material for use in real-time monitoring of crack initiation and propagation in both metallic and composite structures.

A Digital Directional Coupler With Applications to Partial Discharge Measurements

This paper presents a digital directional coupler (DDC) that separates forward- and backward-traveling waves on a transmission line. Based on two independent wideband measurements of voltage and current and on frequency-domain digital wave splitting using a fast Fourier transform (FFT), the DDC is a versatile device for direction separation. A practical procedure is described for the calibration of the digital processor with respect to the particular transmission line and the voltage and current sensors that are being used. As an experiment, a DDC was designed and implemented using low-cost wideband sensors and was installed with medium-voltage equipment in a power distribution station. Partial discharge (PD) measurements were conducted on cross-linked polyethylene (XLPE)-insulated power cables to illustrate the directional separation capabilities of the DDC.

Solid‐State Electrochemical Gas Sensors

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Effect of Sulfuric Acid Concentration on Acoustic Emission Signals in Uniform-Corrosion

In petroleum industry, corrosion failures of steel structures are common. The severity of corrosion in oil distillery inorganic compounds is higher than in those of organic compounds. Inorganic compounds such as sulfur are the most influential corrosive activators inside oil or chemical storage tanks. They normally have the tanks inspected and repaired along their life time. In addition the concentration of sulfur compound increases due to the accumulation of the residuals inside the tank, and so does the corrosive rate. In this paper, Acoustic Emission (AE) has been chosen to study the characteristic of AE signals received from the uniform corrosion mechanism of mild steel (A36) in various concentrations of Sulfuric acid (H2SO4) solution. AE signals were captured using a wide band sensor (WD) and recorded by AE system model LOCAN 320. The relationship between AE signals and sulfur concentrations as well as pH were exhibited.

Performance of energy-aware and link-adaptive routing metrics for ultra wideband sensor networks

Wireless sensor networks are energy constrained since sensors operate with limited battery capacity. Thus, energy consumption is one of the most critical issues in the design of routing protocols. In addition, the link quality needs to be taken into account in the route decision for a wireless multihop network in order to efficiently exploit the inherent spatial diversity. In this paper we consider energy-aware and link-adaptive routing strategies for UWB (Ultra Wide Band) sensor networks. We utilize the ranging capabilities offered by UWB and employ adaptive modulation to take advantage of favorable link conditions. Different routing metrics are proposed based on the availability of sensor node's location, link quality and next hop battery capacity information. These routing metrics integrate the measure of next hop remaining battery capacity with the throughput performance measures, Maximum Forward Progress (MFP) or Maximum Information Progress (MIP). The effectiveness of these metrics is evaluated in different simulation scenarios in terms of network throughput and lifetime for both random and grid sensor network topologies.

An affordable multispectral imaging system for the digital museum

The use of multispectral imaging for the acquisition of the image content of a digital museum is proposed. The advantages of multispectral imaging over “traditional” RGB imaging are explained, and the two existing approaches to multispectral acquisition, based on narrowband and wideband sensors respectively, are detailed. The characteristics of wideband multispectral acquisition systems in view of their possible large-scale use for digital museum content acquisition are then discussed, and an example system assembled by the authors and tested in acquisitions of real artifacts is introduced. Finally, it is shown that multispectral representations collected with such systems can be used for several purposes, including reproduction with current and future devices and support for monitoring and restoration, making them a natural choice for master copies in cultural institutions’ archives.

Blind channel estimation and equalization in wireless sensor networks based on correlations among sensors

In densely deployed wireless sensor networks, signals of adjacent sensors can be highly cross-correlated. This paper proposes to utilize such a property to develop efficient and robust blind channel identification and equalization algorithms. Blind equalization can be performed with complexity as low as O(N/spl tilde/), where N/spl tilde/ is the length of equalizers. Transmissions can be more power and bandwidth efficient in multipath propagation environment, which is especially important for wideband sensor networks such as those for acoustic location or video surveillance. The cross-correlation property of sensor signals and the finite sample effect are analyzed quantitatively to guide the design of low duty-cycle sensor networks. Simulations demonstrate the superior performance of the proposed method.